1. Field of the Invention
The invention relates to mechanisms for dispensing granular materials and, more particularly, to a dispensing mechanism including a hopper and a vertically extending, power-rotated auger that dispenses materials from the hopper in measured quantities.
2. Discussion of the Related Art
Dispensing mechanisms of the type mentioned in Section 1. above are well known in the art. They can be used to dispense virtually any granular particulate materials ranging from relatively course granules such as beans and popcorn down to very fine particles such as cake mixes and pharmaceuticals. Materials to be dispensed are stored in a frusto-conical hopper having a central lower opening through which extends the lower or flight-bearing end portion of an auger. The upper end portion of the auger is in turn rotatably coupled to a drive mechanism such an electrical motor and clutch assembly. In the typical arrangement, the drive mechanism is mounted directly above the central opening of the hopper, and an output shaft of the servo assembly is coupled to an adapter shaft which is in turn coupled to the auger shaft by a quick-connect coupling which permits periodic removal of the auger for replacement, cleaning, etc.
The most prevalent technique for connecting the auger shaft to the adapter shaft (or to another drive shaft if a drive mechanism lacking an adapter shaft is utilized) is a bayonet coupling. Referring to FIGS. 1 and 1A, the typical bayonet coupling 20 includes a male portion and a female portion. The female portion includes a pocket 26 formed in the lower axial end of the adapter shaft 24. A pair of radially opposed, axially extending slots 28 are formed in the peripheral wall of the pocket 26 and terminate in respective peripheral slots 30. Each peripheral slot 30 extends from an inner, relatively narrow section to an outer section of increased diameter serving as a detent 32. The male portion includes the upper end portion of the adapter shaft 22 and a pair of pins 34 located radially opposite one another and extending radially away from the upper end portion of the auger shaft 22.
In use, the upper end portion of the auger shaft 22 is aligned with the lower end portion of the adapter shaft 24 such that the pins 34 are aligned with the axial slots 28. The auger shaft 22 is then lifted into the pocket 26 so that the pins 34 move upwardly through the axial slots 28 into alignment with the opening of the peripheral slots 30. The auger shaft 22 is then rotated so that the pins 34 move into the peripheral slots 30 and drop into the detents 32. The pins 34 are retained in this position by a downward biasing force applied to the auger shaft 22 by a helical spring 36 mounted in a spring chamber 38 located above the slots 30.
While bayonet couplings of the disclosed type provide an effective mechanism for connecting a dispensing auger shaft to an adapter shaft or other drive shaft, they exhibit marked drawbacks and disadvantages.
For instance, it is essential in a variety of applications that the dispensing mechanism be kept as clean as possible and that it be thoroughly cleaned at relatively frequent intervals. However, bayonet couplings are prone to contamination because the materials being dispensed can become tightly lodged between the coils of the return spring and in other areas of the spring chamber. Once these materials are impacted, they are difficult to remove because the return spring prevents a brush or other cleaning implement from being inserted into the spring chamber.
Moreover, during the course of operation of the dispensing mechanism, the ejection of material from the hopper imposes a corresponding upward thrust on the auger as illustrated by the arrow in FIG. 1A. If this upward thrust is strong enough to overcome the biasing forces of the spring, the auger shaft may move upwardly to lift the pins from the base of the detent and, upon subsequent rotation of the auger, may actually become uncoupled from the adapter shaft. Upward movement of the auger also widens the gap between the auger and a lip formed at the bottom of the hopper spout, resulting in loss of accuracy and material drip problems.
Another problem associated with vertical movement of the auger shaft with respect to the adapter shaft is that it imposes backlash on the drive mechanism. Backlash is undesirable, particularly if the drive mechanism comprises a servo assembly, because drive mechanisms in general and servo assemblies in particular do not operate well under the imposition of shifting loads.
Some in the art have addressed the problem of auger shaft movement by affixing a split collar or some other clamp-like device to the auger shaft directly beneath the adapter shaft, thereby preventing vertical movement of the auger shaft with respect to the adapter shaft. However, attachment and removal of the split collar to and from the auger shaft are rather difficult operations because the collar is located in a relatively inaccessible location deep within the hopper. Removal under operational conditions is especially difficult because materials in the hopper inhibit or even prevent access to the split collar. Moreover, the split collar, like the spring chamber, presents crevices in which materials may compact and which are difficult to decontaminate.
Attempts have been made to solve some of the problems associated with conventional bayonet couplings. For instance, U.S. Pat. No. 5,170,914 to Shalit (the Shalit patent) discloses an auger shaft quick-connect coupling which lacks a return spring or a detent. The coupling includes 1) a first sleeve which is secured to the upper end of the auger shaft and 2) a cylindrical shank which is formed integrally with the lower end portion of the drive or adapter shaft and which is sized to snugly fit into a bore formed in the sleeve. A generally T-shaped slot is formed in the lower end portion of the shank and receives a pin fixed rigidly in the sleeve. The auger is attached to the shaft by positioning the auger such that the sleeve is spaced beneath the shank, and the auger is then shifted upwardly to cause the sleeve to telescope into the shank so that the pin passes upwardly within the stem of a T-shaped slot and enters the cross portion thereof. Subsequent rotation of the sleeve causes the pin to move out of alignment with the stem and into the cross portion of the slot. In order to transmit torque from the shaft to the auger, a tube is additionally provided which, when in an active position, rotatably couples the shaft to the auger. A square bore, formed in the tube, receives a complimentary square portion formed in the lower end of the adapter shaft above the shank.
The arrangement disclosed in the Shalit patent, though lacking the springs of conventional bayonet couplings, is relatively complex and difficult to fabricate and to assemble. Moreover, like bayonet couplings, some movement of the auger shaft relative to the adapter or drive shaft appears to be possible after assembly.
Another drawback of conventional dispensing mechanisms is that the connection of the adapter shaft to the motor output shaft is rather complex. It is desirable to provide this connection with the capability to be vertically adjusted so as to facilitate the use of different auger shafts. Traditionally, this vertical adjustment is effected by way of a left hand-threaded connection between the output shaft and the adapter shaft. This connection is rather difficult and expensive to fabricate.